ath5k: use short preamble when possible

ath5k previously ignored TX_RC_SHORT_PREAMBLE and did not use
config->use_short_preamble, so the long preamble was always
used for transmitted packets.

Changes-licensed-under: 3-Clause-BSD
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath5k/base.c

@@ -1179,6 +1179,8 @@ ath5k_txbuf_setup(struct ath5k_softc *sc, struct ath5k_buf *bf)
 	struct ieee80211_rate *rate;
 	unsigned int mrr_rate[3], mrr_tries[3];
 	int i, ret;
+	u16 hw_rate;
+	u8 rc_flags;
 
 	flags = AR5K_TXDESC_INTREQ | AR5K_TXDESC_CLRDMASK;
 
@@ -1186,9 +1188,15 @@ ath5k_txbuf_setup(struct ath5k_softc *sc, struct ath5k_buf *bf)
 	bf->skbaddr = pci_map_single(sc->pdev, skb->data, skb->len,
 			PCI_DMA_TODEVICE);
 
+	rate = ieee80211_get_tx_rate(sc->hw, info);
+
 	if (info->flags & IEEE80211_TX_CTL_NO_ACK)
 		flags |= AR5K_TXDESC_NOACK;
 
+	rc_flags = info->control.rates[0].flags;
+	hw_rate = (rc_flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE) ?
+		rate->hw_value_short : rate->hw_value;
+
 	pktlen = skb->len;
 
 	if (info->control.hw_key) {
@@ -1198,7 +1206,7 @@ ath5k_txbuf_setup(struct ath5k_softc *sc, struct ath5k_buf *bf)
 	ret = ah->ah_setup_tx_desc(ah, ds, pktlen,
 		ieee80211_get_hdrlen_from_skb(skb), AR5K_PKT_TYPE_NORMAL,
 		(sc->power_level * 2),
-		ieee80211_get_tx_rate(sc->hw, info)->hw_value,
+		hw_rate,
 		info->control.rates[0].count, keyidx, 0, flags, 0, 0);
 	if (ret)
 		goto err_unmap;